Download PDF version (4772.5k). The full text of this article is available as a PDF document.

In the Southwest, as well as across the country, architectural block has become the masonry producer's hot product. Producers are challenged to meet tough job-by-job coloring requirements but also produce units in small, custom batches more efficiently.

So in Albuquerque, N.M., when CSR Crego Block's Tim Robertson and his crew recently identified top priorities to erect a new plant, water management was at the top.

Robertson's concern about moisture was twofold.

  • a sure-fire method to cast blocks with more consistent colors
  • to increase his production efficiency by focusing on the water/cement ratio of each mix design

"The colored block market has exploded in the Southwest, quickly becoming our largest market segment," says Robertson. "By focusing on moisture control, and consequently water/cement ratio, in our design process we knew would not only increase the quality of our architectural blocks, but also boost the block line's efficiency, even on short runs."

The significance of this once-in-a-lifetime opportunity plant upgrade was not lost on Robertson. Recently appointed the plant manager, he had spent his career in a plant built in the 1950s. Originally designed for a market half the current size, it had been a proven performer in gray block production. That's not to say there weren't some operational problems to overcome.

CSR Crego currently markets a medium lightweight and a super-lightweight unit in addition to its standard 8-inch block. Accordingly, the company is increasing the volume of volcanic pumice. Since pumice is lighter and more porous than conventional aggregates, the plant operator must follow special handling procedures for proper batching. CSR Crego Block must batch the pumice when it's fully wetted in the stockpile.

Pumice use necessitates another special handling procedure. Since it's lighter, it's less dense than normal aggregate, making it difficult to switch from one aggregate to the other. "Without a scale or batcher, it was difficult to monitor the moisture content of the aggregate and make the mix design adjustments needed for tight architectural coloring, especially when the jobs didn't last too long," said Robertson.

To solve these wide-ranging issues, from the marketing constraints of more architectural blocks to shorter production runs to the production-handling problems due to the pumice, Robertson knew he needed a fully automated plant. The automated plant also had to be flexible enough to make changes in batch water additions quickly because of the short-run nature of the architectural block business.

With the help of its process equipment suppliers, CSR Crego Block's operation team recast each function of the new plant around this water demand control theme. It first reviewed batching parameter changes when switching from mix designs based on volumetric proportioning to ones based on water/cement ratio. Then the team found a way to begin the water-batching process on the new eight-bin feed system.

To handle the pumice's prewetting constraint, engineers added a fail-safe system to allow the batch controller to automatically calculate the material's actual density.

Along with these feed system checks and balances, a microwave moisture sensor is mounted in one of the pan mixer's bottom liners.

CSR Crego Block engineers also selected a granulated color pigment batching system. If conditions warrant it, the producer can program the automated control system to first dry-load all aggregates and pigments into the mixer. Then the system can compare the actual moisture content to a calculated value based upon the input of the feed system sensors.

With such an emphasis on hitting the correct moisture content before final mixing, the process creates a very consistent product slump.

Another probe in the block machine's feed hopper senses how much material is in the hopper and signals the feed conveyor's programmer. Also, the conveyor is programmed to operate at seven preset feed rates.

Another advantage to more consistent concrete uniformity is increased productivity. "A plant operator can easily preset based on the frequency of the packing vibrators based upon the water/cement ratio and thus calibrate the entire block-making process downstream from the feed hopper," says Robertson.